Golden Gate hears concerns over Stinson Beach septic overhaul

02/05/2015

Neighbors had another chance to air their thoughts about a planned overhaul of the Stinson Beach septic system last week, more than a month after the public comment period ended, on Dec. 12. Remarks from the 30 or so residents who attended last Thursday’s presentation by Golden Gate National Recreation Area’s civil engineer Chris Carpenter ranged from the data behind the project to the effects the infrastructure could have on the area.

Mr. Carpenter outlined the $2.35 million project, which represents the National Park Service’s first major effort to prevent rising sea levels from causing coastal groundwater contamination at Stinson Beach.

“We’re trying to be proactive, not reactive,” he said. “We know the groundwater table is coming up, and we want to minimize that risk.”

The beach’s septic system, which serves a million visitors a year, consists of several septic tanks set at four different sites strung along the beach that receive wastewater from the public bathrooms. Collectively called a primary treatment system, these tanks were built in 1960 and are “at or near failure,” Mr. Carpenter said. They will all be replaced or repaired, and relocated further from the beach.

Each original septic tank has its own leach field that allows wastewater to percolate into the ground and, in doing so, be cleansed of contaminants. The problem, according to Mr. Carpenter, is that the soils used for these leach fields do not clean wastewater efficiently enough to safeguard against future groundwater contamination. Many have failed in the past, he said.

To correct this problem, the park service plans to add a secondary treatment facility that will put wastewater effluent through an additional, multi-step cleaning process.

Wastewater collected in the individual tanks will be pumped to three 35-by-7 foot equalization tanks, called “pods,” hidden by a fence and foliage behind the beach’s south parking lot. After passing through aerobic treatment, the wastewater will be stored in two new 5,000-

gallon holding tanks buried underground nearby. From there, wastewater will be pumped through an underground main pipe to a large pressurized leach field to be built in a vacant parcel east of Highway 1.

Some residents at last week’s meeting, which was hosted by the county water district board and held at the community center, were worried about sounds, smells and possible leaks from the proposed infrastructure. 

“The pipe is going to be behind our house,” said Joan Donelan, who has split time between Berkeley and her home on Marine Way since 1983. “What if there was a leak?” Once installed, the three-inch thick high-density polyethylene pipe will run 500 feet along an access road and Marine Way, where Ms. Donelan and several Stinson Beach residents own homes. Mr. Carpenter told residents that the system would be shut down in the event of an earthquake, and noted that the sounds and smells would be minimal.

“The secondary treatment system is set up so that wastewater doesn’t sit for long periods of time,” he said. “If it sits for long periods of time, that’s when you get those smells. And all the pumps are enclosed inside an inch-thick steel wall. It’ll be about 50 decibels, which is pretty quiet.”

Others were curious whether the park knew exactly how high the subterranean water table had actually risen. 

Mr. Carpenter said the park performed percolation tests at five or six sites to evaluate the speed at which wastewater might pass through the ground, but had not determined the height of the water table.

Mr. Carpenter went on to argue that secondary treatment would create a safer “cushion” between wastewater effluent and the underground water table, regardless of the table’s actual height. 

County and Stinson Beach Water District code, he said, require that wastewater treated only by a primary system percolate through the ground for at least 20 feet before reaching the water table; with a secondary system in place, Mr. Carpenter noted, wastewater will be so clean that it will only be required to have a minimum buffer of three feet.

“When we talk about ‘clean’ effluent, it will be very clean,” said Mr. Carpenter, who is in his first year at Golden Gate after working as an engineer for Sequoia and Kings Canyon National Parks. “No chemicals. Low maintenance. And that’s the beauty of it: it’s reliable.”

Resident Steve Simac wondered why the park had not drafted an environmental impact statement for the project. Mr. Ortega replied that the effects of would not merit an impact report under the National Environmental Policy Act.

“This project does not have significant impacts,” Mr. Ortega reiterated in an email after the meeting. “The impacts identified for this project are minor or less than minor.”

Another resident, Jim Gillam, pointed out that the leach field would be built adjacent to his house in an area where shrubs and 100-year old cypress trees provide aesthetic enjoyment and neighborly privacy. 

According to the plan, trees at the center of the leach field parcel will be cut down, while trees around the perimeter will be left and surrounded by new shrubs.“I’m really concerned that it not look like a disposal field, but like a park,” Mr. Gillam said. “But the neighborhood is going to change, and we need to be prepared for that.”